The mammalian hypusine-containing protein, eukaryotic initiation factor 4D. Structural homology of this protein from several species

A single cellular protein of Mr approximately 18,000 and pI near 5.1, recently identified as eukaryotic translation initiation factor eIF-4D, contains the unusual amino acid hypusine N epsilon-(4-amino--2-hydroxybutyl)lysine] formed post-translationally from lysine with a structural contribution from the polyamine spermidine. When the 3H-labeled hypusine-containing protein isolated from Chinese hamster ovary (CHO) cells that were grown with radioactive polyamine is digested with trypsin and the digest is subjected to two-dimensional separation, a single radioactive peptide is seen. A labeled peptide that occupies this same position is found in a digest of the 3H]hypusine protein from human lymphocytes and the single hypusine-containing tryptic peptide from purified rabbit reticulocyte eIF-4D also moves to this identical position. Stepwise Edman degradation of the tryptic digest of CHO cell hypusine-protein releases the radioactivity as a single peak in accordance with our earlier evidence for a single hypusine residue per molecule of eIF-4D. The similar patterns of radioactive peptides obtained from tryptic digests of radioiodinated eIF-4D from CHO cells, human lymphocytes, and rabbit reticulocytes suggest a highly conserved primary structure for this protein.